Present telecommunication system technology includes a wide variety of wireless networking systems associated with both voice and data communications. An overview of several of these wireless networking systems is presented by Amitava Dutta-Roy, Communications Networks for Homes, IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roy discusses several communication protocols in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping (FHSS) protocols. A disadvantage of these protocols is the high overhead associated with their implementation. Id. pg. 31. A less complex wireless protocol known as Shared Wireless Access Protocol (SWAP) also operates in the 2.4 GHz band. This protocol has been developed by the HomeRF Working Group and is supported by North American communications companies. The SWAP protocol uses frequency-hopping spread spectrum technology to produce a data rate of 1 Mb/sec. Another less complex protocol is named Bluetooth after a 10th century Scandinavian king who united several Danish kingdoms. This protocol also operates in the 2.4 GHz band and advantageously offers short-range wireless communication between Bluetooth devices without the need for a central network.
The Bluetooth protocol provides a 1 Mb/sec data rate with low energy consumption for battery powered devices operating in the 2.4 GHz ISM (industrial, scientific, medical) band. The current Bluetooth protocol provides a 10-meter range and an asymmetric data transfer rate of 721 kb/sec. The protocol supports a maximum of three voice channels for synchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetooth protocol treats all radios as peer units except for a unique 48-bit address. At the start of any connection, the initiating unit is a temporary master. This temporary assignment, however, may change after initial communications are established. Each master may have active connections of up to seven slaves. Such a connection between a master and one or more slaves forms a “piconet.” Link management allows communication between piconets, thereby forming “scatternets.” Typical Bluetooth master devices include cordless phone base stations, local area network (LAN) access points, laptop computers, or bridges to other networks. Bluetooth slave devices may include cordless handsets, cell phones, headsets, personal digital assistants, digital cameras, or computer peripherals such as printers, scanners, fax machines and other devices.
The Bluetooth protocol uses time-division duplex (TDD) to support bi-directional communication. Spread-spectrum technology or frequency diversity with frequency hopping permits operation in noisy environments and permits multiple piconets to exist in close proximity. The frequency hopping scheme permits up to 1600 hops per second over 79 1-MHZ channels or the entire ISM spectrum. Various error correcting schemes permit data packet protection by ⅓ and ⅔ rate forward error correction. Further, Bluetooth uses retransmission of packets for guaranteed reliability. These schemes help correct data errors, but at the expense of throughput.
The Bluetooth protocol is specified in detail in Specification of the Bluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporated herein by reference.
In conjunction with frequency hopping systems such as the Bluetooth system, master-slave frequency dwelling (MSD) has been presented as a way of increasing the range in a Bluetooth system when the Doppler frequency is very low. The basic idea is to exploit the frequency diversity of the ISM bands by dwelling on good frequencies that are not currently in a fade. This can extend the operational range of the system by a factor of 3. Such master-slave dwelling techniques are disclosed in copending U.S. Ser. No. 09/507,134 filed on Feb. 22, 2000, incorporated herein by reference.
The aforementioned master-slave frequency dwelling technique is illustrated generally in the Bluetooth example of FIG. 1. MSD is used during the period of time indicated at 11. During this period of time (of length Ti), communications between the master and slave devices are conducted on a single, predetermined dwell frequency. Outside of the MSD time period 11, the frequencies of the normal Bluetooth frequency hopping pattern are used.
In many packet data applications, for example packet data applications in Bluetooth systems, the data will come in large bursts, for example images to download from a digital camera, transmission of a data file, Internet browsing, etc. In many of these situations, the user must wait for a considerable period of time before the entire data transmission is completed. For example, when transmitting a 1 megabyte file with a ⅔ rate code using 3-slot Bluetooth packets (e.g., Bluetooth DM3 packets with 121 information bytes per packet) where the master and slave alternate transmissions (and the acknowledgment takes a single-slot packet) the complete transmission will take about 22 seconds.
In other applications such as Bluetooth HV1 (High-quality Voice) where the voice transmission is protected by a ⅓ rate FEC (forward error correcting code) so that the master and slave each send an HV1 packet every 2 time slots, a single HV1 voice call disadvantageously occupies all of the available time slots.
In any packet communication system, some packets are more important than others, so different packets can have different quality-of-service requirements. In Bluetooth systems, for example, different coding rates are available for voice (rates of ⅓, ⅔ and 1) and for data (rates of ⅔ and 1), so some differentiation in quality-of-service is already possible. One problem, however, is that there is no additional coding across frequencies, so a packet may be lost during a fade, no matter what coding rate is used. Another problem is that using a ⅓ or ⅔ rate code disadvantageously decreases the information rates significantly. Retransmissions, for example using conventional ARQ techniques, are useful for packets that can tolerate the extra delay, but this also disadvantageously reduces the information rate.
It is desirable in view of the foregoing discussion to provide for reducing data transmission times for large data bursts, temporarily freeing time slots in applications which otherwise use all available time slots, and enhancing the quality-of-service for selected packets without decreasing the associated information rate.
The present invention uses master-slave frequency dwelling for selected types of data transmissions such as large data bursts and data requiring an enhanced quality of service. For a large data burst, master-slave frequency dwelling can be combined with an increase in the data transmission rate advantageously to reduce the transmission time of the burst. Also according to the present invention, master-slave frequency dwelling can be combined with an increased data transmission rate advantageously to free time slots which would not otherwise be available.